Mechanical Loading Conditions Research Articles

Skeletal muscle fiber type-specific expressions of mechanosensors integrin-linked kinase, talin, and vinculin and their modulation by loading and environmental conditions in humans.

Mechanosensors control muscle integrity as demonstrated in mice. However, no information is available in human muscle about the distribution of mechanosensors and their adaptations to mechanical loading and environmental conditions (hypoxia). Here, we hypothesized that mechanosensors show fiber-type-specific distributions and that loading and environmental conditions specifically regulate mechanosensors. We randomly subjected 28 healthy males to one of the following groups (n=7 each) consisting of nine loading sessions within 3 weeks: normoxia moderate (NM), normoxia intensive (NI), hypoxia moderate (HM), and hypoxia intensive (HI). We took six biopsies: pre (T0), 4h (T1), and 24 h (T2) after the third as well as 4h (T3), 24 h (T4), and 72 h (T5) after the ninth training session. We analyzed subjects' maximal oxygen consumption (V̇O2 max), maximal power output (Pmax), muscle fiber types and cross-sectional areas (CSA), fiber-type-specific integrin-linked kinase (ILK) localizations as well as ILK, vinculin and talin protein and gene expressions in dependence on loading and environmental conditions. V̇O2 max increased upon NM and HM, Pmax upon all interventions. Fiber types did not change, whereas CSA increased upon NI and HI, but decreased upon HM. ILK showed a type 2-specific fiber type localization. ILK, vinculin, and talin protein and gene expressions differed depending on loading and environmental conditions. Our data demonstrate that mechanosensors show fiber type-specific distributions and that exercise intensities rather than environmental variables influence their profiles in human muscles. These data are the first of their kind in human muscle and indicate that mechanosensors manage the mechanosensing at a fiber-type-specific resolution and that the intensity of mechanical stimulation has a major impact.

Fracture analysis of functionally graded material reinforced with MWCNT

Computational model based on extended isogeometric analysis is implemented for the fracture analysis of functionally graded material (FGM) reinforced with multi-walled carbon nanotube (MWCNT), i.e., FGM-MWCNT structure under mechanical and thermo-mechanical loading conditions. The FGM body taken for the study is composed of metal (Ti–6Al–4V) on the left side and ceramic (ZiO2) on right side. For the gradation of FGM properties that change throughout the domain length, exponential law is assumed. Moreover, the FGM is reinforced with 0–5% of MWCNT to obtain FGM-MWCNT composite. In order to perform this fracture analysis, first the equivalent mechanical and thermal properties of the FGM-MWCNT composite are evaluated using some of the micromechanics models cited in the literature. Using the interaction integral approach, SIFs are extracted. The results of the test show that when the volume percentage of MWCNTs increases, it enhances the failure resistance of the composite.

Atomistic Investigation on the Strengthening Mechanism of Single Crystal Ni-Based Superalloy under Complex Stress States

Single crystal Ni-based superalloy, with excellent mechanical properties in high temperature, always works under complex stress states, including multiaxial tension and compression, which results in various strengthening mechanisms. In this paper, the atomistic simulation is applied to investigate the microstructure evolution under complex mechanical loading conditions, including uniaxial, equibiaxial, and non-equibiaxial tensile–compressive loadings. By comparison of the strain–stress curves and analysis of dislocation motion, it is believed that the tension promotes the bowing out of dislocations into the channel at loading direction, while compression limits it. Moreover, the dislocation analysis shows that the initial dislocation network, comprised of Lomer dislocations, will dissociate to form Lomer–Cottrell lock upon loading, which acts as a barrier to the further glide of dislocations. The mechanism of dislocation evolution is analyzed in detail by combining Schmid factor analysis and the comparison of energy density difference between γ and γ′ phases.

Investigating the graded-index influence on elastic responses of axisymmetric pressurized and heated thick-walled functionally graded material of cylindrical vessel

This article presents the influence of a graded-index on the elastic responses of an axisymmetric pressurized and heated thick-walled functionally graded material (FGM) cylindrical vessel under plane strain conditions. It is assumed that the inside surface/outside surface of a cylinder is made up of ceramic /metal. The temperature-independent thermo-mechanical parameters of an FGM cylinder are described by using the rule-of-mixture with the function of radius. The profiles of thermo-mechanical material characteristics are assumed to vary continuously and gradually along the thickness direction of a cylinder. The numerical solutions of the thick-walled FGM cylinder governing differential equations are examined by using the non-linear shooting and fourth-order Runge-Kutta approaches. The thermo-elastic solutions of the thick-walled FGM cylinder over the radial direction are computed using Jupiter, Python open-access software, and graphically reported. The analytical solutions (AS) of a ceramic cylinder are compared with numerical solutions (NS) of an FGM cylinder (n = 0) to validate the proposed method. The results reveal that the graded-index n has a higher influence on the profiles of dimensionless hoop stress, dimensionless axial stress, dimensionless radial displacement, hoop strain, radial strain, and thermo-mechanical material properties in the dimensionless radial direction of an FGM cylinder. Nevertheless, the graded-index has an insignificant impact on dimensionless radial stress across the dimensionless radial direction of an FGM cylinder. Based on these findings, it is recommended that graded-index is an important parameter which can be used to regulate the responses of FGM structures under thermal and mechanical loading conditions.

Bearing capacity and durability of rolling bearings of technical systems

The influence of mechanical loading conditions and the state of the contact surface of the working bodies of rolling bearings on their bearing capacity and durability are considered. It is shown that the existing assessment of the bearing capacity and durability of rolling bearings is made on the basis of standard calculations that do not take into account the action of friction forces arising at the site of contact of rolling bodies with the ring track, and heat generation in the contact zone of working bodies. It is proved that the choice of rolling bearings should be carried out according to the specifi ed dynamic load capacity curve, taking into account the conditions of mechanical loading, the infl uence of the temperature factor and the coeffi cient of dynamism on the durability of bearings in the operating temperature range for the lubricant used.

Shape Memory Alloy-Polymer Composites: Static and Fatigue Pullout Strength under Thermo-Mechanical Loading.

This work was carried out within the context of an R&D project on morphable polymer matrix composites (PMC), actuated by shape memory alloys (SMA), to be used for active aerodynamic systems in automotives. Critical issues for SMA–polymer integration are analyzed that are mostly related to the limited strength of metal–polymer interfaces. To this aim, materials with suitable thermo-mechanical properties were first selected to avoid premature activation of SMA elements during polymer setting as well as to avoid polymer damage during thermal activation of SMAs. Nonstandard samples were manufactured for both static and fatigue pullout tests under thermo-mechanical loading, which are made of SMA wires embedded in cylindrical resin blocks. Fully coupled thermo-mechanical simulations, including a special constitutive model for SMAs, were also carried out to analyze the stress and temperature distribution in the SMA–polymer samples as obtained from the application of both mechanical loads and thermal activation of the SMA wires. The results highlighted the severe effects of SMA thermal activation on adhesion strength due to the large recovery forces and to the temperature increase at the metal–polymer interface. Samples exhibit a nominal pullout stress of around 940 MPa under static mechanical load, and a marked reduction to 280 MPa was captured under simultaneous application of thermal and mechanical loads. Furthermore, fatigue run-out of 5000 cycles was achieved, under the combination of thermal activation and mechanical loads, at a nominal stress of around 200 MPa. These results represent the main design limitations of SMA/PMC systems in terms of maximum allowable stresses during both static and cyclic actuation.

The mechanics of initiation and development of thrust faults and thrust ramps

This study integrates the results of numerical modeling analyses based on outcrop studies and structural kinematic restorations to evaluate the mechanics of thrust fault initiation and development in mechanically layered sedimentary rocks. A field-based reconstruction of a mesoscopic thrust fault at Ketobe Knob in central Utah provides evidence of thrust ramp nucleation in competent units, and fault propagation upward and downward into weaker units at both fault tips. We investigate the effects of mechanical stratigraphy on stress heterogeneity, rupture direction, fold formation, and fault geometry motivated by the geometry of the Ketobe Knob thrust fault in central Utah; the finite element modeling examines how mechanical stratigraphy, load conditions, and fault configurations influence temporal and spatial variation in stress and strain. Our modeling focuses on the predicted deformation and stress distributions in four model domains: (1) an intact, mechanically stratified rock sequence, (2) a mechanically stratified section with a range of interlayer frictional strengths, and two faulted models, (3) one with a stress loading condition, and (4) one with a displacement loading condition. The models show that early stress increase in competent rock layers are accompanied by low stresses in the weaker rocks. The frictional models reveal that the heterogeneous stress variations increase contact frictional strength. Faulted models with a 20° dipping fault in the most competent unit result in stress increases above and below fault tips, with extremely high stresses predicted in a ‘back thrust’ location at the lower fault tip. These findings support the hypothesis that thrust faults and associated folds at the Ketobe Knob developed in accordance with a ramp-first kinematic model and development of structures was significantly influenced by the nature of the mechanical stratigraphy.

BISON validation of FeCrAl cladding mechanical failure during simulated reactivity-initiated accident conditions

A reactivity-initiated accident (RIA) is a postulated design basis accident in light water reactors (LWRs) in which a rapid reactivity insertion induces a fission rate increase and a fuel pellet temperature rise. During RIA, the fuel pellet thermally expands and may cause pellet-cladding mechanical interaction (PCMI). Separate effects PCMI tests were performed on C26M FeCrAl cladding tube samples, introducing biaxial stress via a well understood modified burst test (MBT) system. A high-speed camera in the MBT system captured the projections, covering a 360° view of the cladding deformation and enabling a digital image correlation (DIC) method to quantify the surface strains with high fidelity. Representative hot zero-power RIA mechanical loading conditions were applied to the sample, and the test duration ranged from 20 to 500 ms at an average temperature of 573 K. BISON finite element–based fuel performance code modeling was performed against the high-fidelity DIC data produced from the MBTs. Validation calculations were conducted with 2D models and systematically compared with test data of the burst time, burst pressure, burst hoop strains, and hoop strain rates. Based on the behaviors from the separate effects test, BISON calculations satisfactorily predicted the cladding deformation behaviors. Sensitivity analysis was conducted to identify highly influential mechanical properties responsible for the cladding failure behavior during the MBT experiments. The results highlight the significance of the cladding's mechanical strength in governing cladding strain, followed by the significance of the mechanical interactions between the pellet and the cladding.

The effects of substrate porosity, mechanical substrate properties and loading conditions on the attachment performance of the Mediterranean medicinal leech (Hirudo verbana).

The ectoparasitic lifestyle of the Mediterranean medicinal leech (Hirudo verbana) requires reliable functioning of its attachment organs (i.e. anterior and posterior suction discs) on multiple habitat- and host-specific surfaces under both normal and shear stresses. In addition to some intrinsic properties of the attachment devices, however, only a few extrinsic factors (e.g. substrate roughness and porosity) have been considered in previous studies on leech suckers. Using centrifugal force experiments, we analysed the attachment performance of H. verbana under different types of loading on artificial substrates differing in porosity and their mechanical properties. Whereas the substrate porosity significantly influenced leech attachment under normal and shear loading, the different mechanical properties did not noticeably affect attachment within the considered parameter limits. Furthermore, suction was confirmed to be the primary attachment mechanism independent of the prevailing loading condition. The question of whether the suction cups of H. verbana are adapted to a specific loading condition could not be answered. In any case, our results again highlight the high functional resilience of leech suckers guaranteeing a successful ectoparasitic lifestyle.

Application of a dynamic thermoelastic coupled model for an aerospace aluminium composite panel

An analytical-numerical coupled model has been derived to predict the effects of dynamic thermo-mechanical loading on aluminium composite panels specifically in the form of metallic skin sandwich structures, for the purposes of enhanced design of spacecraft structures where the environmental conditions comprise combined mechanical and thermal loading. The mechanical loading can arise as a consequence of localised structural dynamics, and the thermal loading is attributable principally to the effects of solar irradiation and eclipse during a satellite’s orbit, and together they have the potential to influence de-point adversely, in particular. On this basis a combined physics model is required to deal with the generalised thermoelastic problem and this paper reports on the theoretical work done to achieve that. The research has considered the literature in detail and a refined model has been proposed for an aerospace application which results in an analytical-numerical solution for the thermoelastic problem in aluminium composite panels. The model is explored for a panel under a range of centrally located static mechanical loads, in conjunction with thermal loading provided in the form of various controlled and elevated environmental temperature functions, all for prescribed physical boundary conditions. Both forms of loading are shown to influence the displacement of the panel significantly, thereby confirming the importance of a combined physics model for analysing structures in this context.

Dependence of Piezoelectric Discs Electrical Impedance on Mechanical Loading Condition

The piezoelectric effect, along with its associated materials, fascinated researchers in all areas of basic sciences and engineering due to its interesting properties and promising potentials. Sensing, actuation, and energy harvesting are major implementations of piezoelectric structures in structural health monitoring, wearable devices, and self-powered systems, to name only a few. The electrical or mechanical impedance of its structure plays an important role in deriving its equivalent model, which in turn helps to predict its behavior for any system-level application, such as with respect to the rectifiers containing diodes and switches, which represent a nonlinear electrical load. In this paper, we study the electrical impedance response of different sizes of commercial piezoelectric discs for a wide range of frequencies (without and with mechanical load for 0.1–1000 with resolution 20 ). It shows significant changes in the position of resonant frequency and amplitude of resonant peaks for different diameters of discs and under varying mechanical load conditions, implying variations in the mechanical boundary conditions on the structure. The highlight of our work is the proposed electrical equivalent circuit model for varying mechanically loaded conditions with the help of impedance technique. Our approach is simple and reliable, such that it is suitable for any structure whose accurate material properties and dimensions are unknown.

Numerical study on cracking and its effect on chloride transport in concrete subjected to external load

Reinforced concrete (RC) structures have been severely threatened by chloride attacks during long-term service, particularly under mechanical loading conditions. This study presents a multi-species and multi-phase model considering the time-dependent cracking in concrete. In addition to the crack propagation and chloride diffusion being individually modelled, these two processes are coupled by statistical learning approach, which is supposed to better reveal the influence of cracking on chloride transport. Meanwhile, the electrostatic potential generated by the inner charge imbalance and its effect on multi-species transport is also considered. The validity of the presented model is verified against third-party experiments following the standard of RILEM TC 246-TDC. The impact of different crack characteristics on chloride transport was carefully elaborated, and the effects caused by multi-species interactions, coupling between cracking and chloride ingress, as well as other environmental factors such as external concentration are also discussed in detail. The findings of presented study can better enhance the understanding on the deterioration of both durability and bearing capacity of RC structures.

Prediction of Internal Circuit and Mechanical-Electrical-Thermal Response of Lithium-Ion Battery Cell with Mechanical-Thermal Coupled Analysis

The lithium-ion battery (LIB) is widely used as an energy storage device for electric vehicles (EV) due to its advantages, such as high energy density and long lifespan. However, LIB for EV can be exposed to mechanical abuse such as vehicle collision, which causes thermal runaway due to extreme mechanical deformation. Therefore, it is necessary to predict the internal short circuit (ISC) of the LIB cell under mechanical loading conditions and to analyze the mechanical, electrical, and thermal responses after ISC. In this paper, the starting point of ISC is predicted using a two-way mechanical-electrical-thermal coupled analysis method. At the same time, mechanical responses, along with the effects of the ISC area on electrical and thermal responses of the LIB cell, were analyzed. ISC was defined as failure of the separator. The separator’s failure was calculated considering material nonlinearity. Considering the indentation test results, the finite element method (FEM) analysis could accurately predict the starting point of ISC. In the order of cylindrical, hemispherical, and conical indenters, ISC occurred quickly, and the ISC area was large. The larger the ISC area, the greater the voltage drop, current, and joule heat, and the higher the maximum temperature.

Parametric Instability of Rotating Functionally Graded Graphene Reinforced Truncated Conical Shells Subjected to Both Mechanical and Thermal Loading Conditions

This article focuses on parametric instability of rotating functionally graded (FG) truncated conical shells reinforced by graphene platelets (GPLs) and subjected to both mechanical and thermal loading conditions. The GPL nanofillers are uniformly dispersed in each concentric conical layer but its weight fraction varies continuously along thickness direction, which induces the position-dependent effective material properties. Based on Love’s thin shell theory and Galerkin approach, the equations of motion for the conical shells are derived with the effects of the periodic axial loads, thermal expansion deformation, rotation-induced initial hoop tension, gyroscopic and centrifugal forces taken into account. Then, the parametric instability under combination parametric resonance for the conical shells is performed by the method of multiple scales, and the analytical solutions of both instability boundaries are obtained. A comprehensive parametric study is conducted which focuses on instability regions and vibration characteristics of the conical shell. Of particular interest in this process is the combined effect of the rotation, dynamic loads and thermal effects on dynamic stability of FG-GPL reinforced truncated conical shells.

Application of two‐layer viscoplasticity model to predict a semicrystalline polymer response under compression and microindentation

AbstractPolymeric materials are widely used in structural components and systems, and the accurate prediction of their complex time‐dependent behavior is critical. Several constitutive models are available for different types of mechanical behaviors and loading conditions. However, selecting the model and the correct calibration of its parameters is often a challenge. This paper evaluates the applicability of the two‐layer viscoplasticity (TLV) model to predict the viscoplastic behavior of polyvinylidene fluoride (PVDF) in a large range of strain rates and complex states of strain. The setting of parameters and model validation was made by performing experimentally and numerically uniaxial compression tests and relaxation tests. The model parameters were also analyzed in performing microindentation tests. The TLV model using the same set of parameters selected well predicted the PVDF behavior in a wide variety of compressive loading conditions.

Electrothermal Performance of Heaters Based on Laser-Induced Graphene on Aramid Fabric.

Nanostructured heaters based on laser-induced graphene (LIG) are promising for heat generation and temperature control in a variety of applications due to their high efficiency as well as a fast, facile, and highly scalable fabrication process. While recent studies have shown that LIG can be written on a wide range of precursors, the reports on LIG-based heaters are mainly limited to polyimide film substrates. Here, we develop and characterize nanostructured heaters by direct writing of laser-induced graphene on nonuniform and structurally porous aramid woven fabric. The synthesis and writing of graphene on aramid fabric is conducted using a 10.6 μm CO2 laser. The quality of laser-induced graphene and electrical properties of the heater fabric is tuned by controlling the lasing process parameters. Produced heaters exhibit good electrothermal efficiency with steady-state temperatures up to 170 °C when subjected to an input power density of 1.5 W cm–2. In addition, the permeable texture of LIG–aramid fabric heaters allows for easy impregnation with thermosetting resins. We demonstrate the encapsulation of fabric heaters with two different types of thermosetting resins to develop both flexible and stiff composites. A flexible heater is produced by the impregnation of LIG–aramid fabric by silicone rubber. While the flexible composite heater exhibits inferior electrothermal performance compared to neat LIG–aramid fabric, it shows consistent electrothermal performance under various electrical and mechanical loading conditions. A multifunctional fiber-reinforced composite panel with integrated de-icing functionality is also manufactured using one ply of LIG–aramid fabric heater as part of the composite layup. The results of de-icing experiments show excellent de-icing capability, where a 5 mm thick piece of ice is completely melted away within 2 min using an input power of 12.8 W.

Chronic Polyhydramnios: A Medical Entity Which Could Be a Model of Muscle Development in Decreased Mechanical Loading Condition.

Polyhydramnios is a condition related to an excessive accumulation of amniotic fluid in the third trimester of pregnancy and it can be acute and chronic depending on the duration. Published data suggest that during muscle development, in the stage of late histochemical differentiation decreased mechanical loading cause decreased expression of myosin heavy chain (MHC) type 1 leading to slow-to-fast transition. In the case of chronic polyhydramnios, histochemical muscle differentiation could be affected as a consequence of permanent decreased physical loading. Most affected would be muscles which are the most active i.e., spine extensor muscles and muscles of legs. Long-lasting decreased mechanical loading on muscle should cause decreased expression of MHC type 1 leading to slow-to-fast transition, decreased number of muscle fiber type I especially in extensor muscles of spine and legs. Additionally, because MHC type 1 is present in all skeletal muscles it could lead to various degrees of hypotrophy depending on constituting a percentage of MHC type 1 in affected muscles. These changes in the case of preexisting muscle disorders have the potential to deteriorate the muscle condition additionally. Given these facts, idiopathic chronic polyhydramnios is a rare opportunity to study the influence of reduced physical loading on muscle development in the human fetus. Also, it could be a medical entity to examine the influence of micro- and hypogravity conditions on the development of the fetal muscular system during the last trimester of gestation.

Cartilage Tissue Engineering Approaches Need to Assess Fibrocartilage When Hydrogel Constructs Are Mechanically Loaded.

Chondrocytes that are impregnated within hydrogel constructs sense applied mechanical force and can respond by expressing collagens, which are deposited into the extracellular matrix (ECM). The intention of most cartilage tissue engineering is to form hyaline cartilage, but if mechanical stimulation pushes the ratio of collagen type I (Col1) to collagen type II (Col2) in the ECM too high, then fibrocartilage can form instead. With a focus on Col1 and Col2 expression, the first part of this article reviews the latest studies on hyaline cartilage regeneration within hydrogel constructs that are subjected to compression forces (one of the major types of the forces within joints) in vitro. Since the mechanical loading conditions involving compression and other forces in joints are difficult to reproduce in vitro, implantation of hydrogel constructs in vivo is also reviewed, again with a focus on Col1 and Col2 production within the newly formed cartilage. Furthermore, mechanotransduction pathways that may be related to the expression of Col1 and Col2 within chondrocytes are reviewed and examined. Also, two recently-emerged, novel approaches of load-shielding and synchrotron radiation (SR)–based imaging techniques are discussed and highlighted for future applications to the regeneration of hyaline cartilage. Going forward, all cartilage tissue engineering experiments should assess thoroughly whether fibrocartilage or hyaline cartilage is formed.

Effect of Nesfatin-1 on Rat Humerus Mechanical Properties under Quasi-Static and Impact Loading Conditions.

The investigations on the response of bone tissue under different loading conditions are important from clinical and engineering points of view. In this paper, the influence of nesfatin-1 administration on rat humerus mechanical properties was analyzed. The classical three-point bending and impact tests were carried out for three rat bone groups: control (SHO), the humerus of animals under the conditions of established osteopenia (OVX), and bones of rats receiving nesfatin-1 after ovariectomy (NES). The experiments proved that the bone strength parameters measured under various mechanical loading conditions increased after the nesfatin-1 administration. The OVX bones were most susceptible to deformation and had the smallest fracture toughness. The SEM images of humerus fracture surface in this group showed that ovariectomized rats had a much looser bone structure compared to the SHO and NES females. Loosening of the bone structure was also confirmed by the densitometric and qualitative EDS analysis, showing a decrease in the OVX bones’ mineral content. The samples of the NES group were characterized by the largest values of maximum force obtained under both quasi-static and impact conditions. The energies absorbed during the impact and the critical energy for fracture (from the three-point bending test) were similar for the SHO and NES groups. Statistically significant differences were observed between the mean Fi max values of all analyzed sample groups. The obtained results suggest that the impact test was more sensitive than the classical quasi-static three-point bending one. Hence, Fi max could be used as a parameter to predict bone fracture toughness.

Experimental Investigation of Performance Characteristics of PZT-5A with Application to Fault Diagnosis

In the previous couple of decades, techniques to reap energy and empower low voltage electronic devices have received outstanding attention. Most of the methods based on the piezoelectric effect to harvest the energy from ambient vibrations have been revolutionized. There’s an absence of experiment-based investigation which incorporates the microstructure analysis and crystal morphology of those energy harvest home materials. Moreover, the impact of variable mechanical and thermal load conditions has seldom been studied within the previous literature to utilize the effectiveness of those materials in several practical applications like structural health monitoring (SHM), etc. In the proposed research work, scanning electron microscope (SEM) and energy dispersive x-ray (EDX) analysis are performed to examine the inside crystal morphology of PZT-5A and ensure the quality of the piezoelectric ceramic. Further, the performance of piezoelectric vibration-based energy harvester has been investigated in the second phase of current research work under the variable mechanical and thermal load conditions through a regular series of experiments. It’s been found that the output voltage of piezoelectric sensors will increase by increasing the applied load, whereas a decreasing trend in output voltage is noticed by increasing the applied temperature, resistance and frequency. Within the third part, a measuring setup is developed in the laboratory to further investigate the effectiveness of PZT-5A in practical applications such as electromechanical impedance (EMI) based structural health monitoring under the controlled heating environment. Therefore, this analysis not only evaluates the performance of PZT sensors under the variable operating conditions but also encourages developing a temperature compensation approach in EMI-based SHM.